Humidification of respiratory gases

Patent metadata

Field	Value
Publication number	US-9802022-B2
Application number	US-39785009-A
Country	US
Kind code	B2
Filing date	Mar 4, 2009
Priority date	Mar 6, 2008
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

A humidifier for a respiratory apparatus for delivering a humidified flow of breathable gas to a patient includes a humidifier chamber configured to store a supply of water to humidify the flow of breathable gas, the humidifier chamber comprising a first heating element configured to heat the supply of water; a relative humidity sensor to detect a relative humidity of ambient air and generate signals indicative of the ambient relative humidity; a first temperature sensor to detect a temperature of ambient air and generate signals indicative of the ambient temperature; and a controller configured to determine an absolute humidity of the ambient air from the signals generated by the relative humidity sensor and the first temperature sensor and to control the first heating element to provide a predetermined relative humidity to the flow of breathable gas. A method of humidifying a flow of breathable gas to be provided to a patient includes determining an absolute humidity of ambient air used to form the flow of breathable gas; and controlling a temperature of a supply of water that humidifies the flow of breathable gas to provide a predetermined absolute humidity corresponding to a predetermined temperature and a predetermined relative humidity of the flow to be delivered to the patient.

First claim

What is claimed is:

1. A humidifier for a respiratory apparatus for delivering a humidified flow of breathable gas to a patient, the humidifier comprising:
a humidifier chamber configured to store a supply of water to humidify the flow of breathable gas, the humidifier chamber comprising a first heating element configured to heat the supply of water;
a humidity sensor to detect an ambient humidity of the patient's environment and generate signals indicative of the ambient humidity; and
a controller configured to receive the signals from the humidity sensor and control the first heating element to provide a predetermined humidity to the flow of breathable gas based on a difference between an ambient absolute humidity corresponding to the detected ambient humidity and a predetermined absolute humidity that corresponds to the predetermined humidity,
wherein the controller is configured to calculate an evaporation rate of the supply of water required to provide the difference between the ambient absolute humidity and the predetermined absolute humidity,
wherein the evaporation rate is determined by multiplying a flow rate of the flow of breathable gas and the difference between the predetermined absolute humidity and the ambient absolute humidity, and
wherein the flow rate corresponds to a vent flow from a patient interface at a pressure of the flow of breathable gas.

2. A humidifier according to claim 1 , wherein the controller is further configured to control the first heating element to provide the flow of humidified breathable gas at a predetermined temperature.

3. A humidifier according to claim 2 , wherein the predetermined humidity is a predetermined relative humidity and the controller is configured to determine the predetermined absolute humidity based on the predetermined relative humidity and the predetermined temperature.

4. A humidifier according to claim 3 , further comprising a user input configured to permit the patient or a clinician to select the predetermined temperature and/or the predetermined relative humidity.

5. A humidifier according to claim 4 , wherein the user input comprises a control knob.

6. A humidifier according to claim 3 , wherein the controller is configured to calculate the ambient absolute humidity according to the formula AHa=RHa·(K 1 −K 2 ·Ta+K 3 ·Ta 2 ), wherein AHa is ambient absolute humidity, RHa is an ambient relative humidity and Ta is an ambient temperature, and is configured to calculate the predetermined absolute humidity according to the formula AHp=RHp·(K 1 −K 2 ·Tp+K 3 ·Tp 2 ), wherein AHp is the predetermined absolute humidity, RHp is the predetermined relative humidity, Tp is the predetermined temperature, and K 1 , K 2 , and K 3 are coefficients.

7. A humidifier according to claim 3 , further comprising a flow rate sensor configured to determine the flow rate and generate signals indicative of the flow rate.

8. A humidifier according to claim 2 , wherein the predetermined temperature is about 15° C.-37° C.

9. A humidifier according to claim 2 , wherein the predetermined temperature is about 26°-28° C.

10. A humidifier according to claim 2 further comprising a user input configured to permit the patient or a clinician to select the predetermined temperature and/or the predetermined absolute humidity.

11. A humidifier according to claim 1 , wherein the predetermined absolute humidity is about 11- 44 mg/L.

12. A humidifier according to claim 1 , wherein the predetermined humidity is a predetermined relative humidity of about 50%-100%.

13. A humidifier according to claim 1 , wherein the predetermined humidity is a predetermined relative humidity of about 70%-90%.

14. A humidifier according to claim 1 , further comprising a temperature sensor to detect a temperature of the supply of water or a temperature of the first heating element and generate signals indicative of the temperature of the supply of water or the temperature of the first heating element, respectively, wherein the controller is configured to control the first heating element in a feedback loop of the signals generated by the temperature sensor.

15. A humidifier according to claim 1 , wherein the controller is configured to control the first heating element to increase the temperature of the supply of water as a flow rate of the flow of breathable gas increases and decrease temperature of the supply of water as the flow rate decreases.

16. A humidifier according to claim 1 , wherein the controller is configured to control the first heating element to decrease the temperature of the supply of water as the ambient absolute humidity increases, and to increase the temperature of the supply of water as the ambient absolute humidity decreases.

17. A humidifier according to claim 1 , wherein the controller is configured to control the first heating element to increase the temperature of the supply of water as a predetermined temperature of the flow of breathable gas increases, and to decrease the temperature of the supply of water as the predetermined temperature of the flow of breathable gas decreases.

18. A humidifier according to claim 1 , wherein a plurality of predetermined temperatures, a plurality of predetermined relative humidities, and a plurality of corresponding predetermined absolute humidities are stored in memory operatively associated with the controller.

19. A humidifier according to claim 1 , further comprising a delivery hose configured to deliver the humidifier flow of breathable gas to the patient, the delivery hose comprising a first end configured for connection to an outlet of the humidifier, a second end configured for connection to a patient interface, and a second heating element configured to heat the humidified flow of breathable gas in the delivery hose.

20. A humidifier according to claim 19 , further comprising a temperature sensor at the second end of the delivery hose configured to detect a temperature of the humidified flow of the breathable gas at the second end of the delivery hose and generate signals indicative of the detected temperature of the humidified flow of the breathable gas at the second end of the delivery hose.

21. A humidifier according to claim 20 , wherein the controller is configured to control the second heating element in response to the signals from the temperature sensor to provide the humidified flow of breathable gas at the second end of the delivery hose at a predetermined temperature and a predetermined relative humidity.

22. A humidifier according to claim 20 , wherein the controller is configured to determine a change in a rate of the humidified flow of breathable gas and control the second heating element to adjust a predetermined temperature of the humidified flow of breathable gas when the change in the flow rate exceeds a predetermined flow rate change.

23. A humidifier according to claim 22 , wherein the controller is configured to control the second heating element to increase the predetermined temperature of the humidified flow of breathable gas when the change in the flow rate exceeds a predetermined decrease in the flow rate.

24. A humidifier according to claim 23 , wherein the controller is configured to control the second heating element to increase the predetermined temperature of the humidified flow of the breathable gas above a saturation temperature.

25. A humidifier according to claim 24 , wherein the controller is configured to control the fir

Assignees

• Smith Ian Malcolm
• Bath Andrew Roderick
• Row Nathan John
• Virr Alexander
• Resmed Ltd

Inventors

• Smith Ian Malcolm
• Bath Andrew Roderick
• Row Nathan John
• Virr Alexander

Classifications

• A61M16/1075 Primary

  by influencing the temperature (A61M16/1045 takes precedence) · CPC title

• A61M2205/3358

  Measuring barometric pressure, e.g. for compensation · CPC title

• A61M16/1095

  in the connecting tubes · CPC title

• A61M2205/3365

  Rotational speed · CPC title

• A61M2205/502

  User interfaces, e.g. screens or keyboards · CPC title